DC-DC converter for wide input voltage

ABSTRACT

A DC-DC converter includes an inductor, a rectifier module, a first bridge arm topology and a second bridge arm topology and a third bridge arm topology in parallel as well as a capacitor, wherein the first bridge arm topology includes a first switching tube and a fourth switching tube in series, the second bridge arm topology includes a second switching tube and a fifth switching tube in series, and the third bridge arm topology includes a third switching tube and a sixth switching tube in series; the inductor has one end connected to a coupling point formed by connecting the first switching tube and the fourth switching tube in series, and the other end connected to a coupling point formed by connecting the second switching tube and the fifth switching tube in series.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to the field of switching power supplies,and more particularly relates to a DC-DC converter.

Description of the Related Art

The DC-DC converter is a widely used power electronic device, whichcontrols on/off of the switches in combination with passive energystorage devices such as inductors and capacitors to convert an inputdirect current into another direct current with a fixed voltage or anadjustable voltage, including direct DC-DC converter and indirectDC-AC-DC converter. The direct DC-DC converter is also known as achopper circuit, and there are six basic chopper circuits: buck choppercircuit (also known as Buck converter), boost chopper circuit (alsoknown as Boost converter), buck-boost chopper circuit (also known asBuck-Boost converter), Cuk chopper circuit, Sepic chopper circuit andZeta chopper circuit. The direct DC converter does not have an isolatedtransformer, while an indirect DC converter is formed by adding an ACpart in the DC converter, that is, an isolated transformer is usuallyprovided between the input and output ends, and thus the indirect DCconverter is also called a DC converter with an isolated transformer. Inthe current switching power supplies, the indirect DC converter is themain structural form in the current applications.

At the same time, in industrial applications, DC voltages with multiplevoltage levels are usually required, and the DC-DC converter withmultiple output ports can achieve more compact structure and saved costwhile meeting the requirement of multi-voltage-level output. Throughrational design, the present invention proposes a DC-DC convertertopology with two output ports based on a basic DC converter.

SUMMARY OF THE INVENTION

In view of the above-described defects or improvement requirements inthe art, the present invention provides a DC-DC converter, which aims tosolve the technical problem that the existing DC-DC converter is nothigh in efficiency and power density.

In order to achieve the above objective, the present invention providesa DC-DC converter, comprising: a DC-DC converter, characterized bycomprising: an inductor, a rectifier module, a first bridge arm topologyand a second bridge arm topology and a third bridge arm topology inparallel as well as a capacitor, wherein the first bridge arm topologyincludes a first switching tube and a fourth switching tube in series,the second bridge arm topology includes a second switching tube and afifth switching tube in series, and the third bridge arm topologyincludes a third switching tube and a sixth switching tube in series; anegative pole of the first bridge arm topology is connected to anegative pole of the second bridge arm topology, and the inductor hasone end connected to a coupling point formed by connecting the firstswitching tube and the fourth switching tube in series, and the otherend connected to a coupling point formed by connecting the secondswitching tube and the fifth switching tube in series;

an input end of the rectifier module has one end connected to thecoupling point formed by connecting the second switching tube and thefifth switching tube in series, and the other end connected to acoupling point formed by connecting the third switching tube and thesixth switching tube in series, and the rectifier module is used toconvert an alternating current into a direct current; there is a phasedifference between a control signal of the second bridge arm topologyand a control signal of the third bridge arm topology;

the first bridge arm topology and the inductor constitute a Buckconverter for stepping down an input voltage, the second bridge armtopology and the inductor constitute a Boost converter for stepping upan input voltage, and the second bridge arm topology, the third bridgearm topology and the rectifier module constitute a phase-shiftedfull-bridge converter for stepping down or stepping up an input voltage;the DC-DC converter multiplexes the inductor and the second bridgetopology.

Preferably, the two ends of the first bridge arm topology serve as an DCinput end of the DC-DC converter, the capacitor serves as a first DCoutput end of the DC-DC converter, and an output end of the rectifiermodule serves as a second DC output end of the DC-DC converter.

Preferably, two ends of the first bridge arm topology serve as a firstDC input end of the DC-DC converter, the capacitor serves as a second DCinput end of the DC-DC converter, and an output end of the rectifiermodule serves as a first DC output end of the DC-DC converter.

Preferably, the rectifier module comprises a transformer and tworectifier diodes, a primary side of the transformer serves as the inputend of the rectifier module, taps on both ends of a secondary side ofthe transformer are each connected in series with a rectifier diode, theother ends of the two rectifier diodes are connected as a first port ofthe output end of the rectifier module, and a center tap of thetransformer serves as a second port of the output end of the rectifiermodule.

Preferably, each of the switching tubes of the first bridge arm topologyis connected in parallel with a diode and a capacitor to enable softswitching of the switching tubes in the first bridge arm topology.

Preferably, the DC-DC converter further comprises a resonant inductorand a DC blocking capacitor, wherein the resonant inductor, the primarycoil of the transformer and the DC blocking capacitor are sequentiallyconnected in series to form a series branch, the series branch has oneend connected to the coupling point formed by connecting the secondswitching tube and the fifth switching tube in series and the other endconnected to the coupling point formed by connecting the third switchingtube and the sixth switching tube in series, and each of the switchingtubes of the second bridge arm topology and the third bridge armtopology is connected in parallel with a diode and a capacitor to enablesoft switching of each of the switching tubes of the second bridge armtopology and the third bridge arm topology.

Preferably, the diodes and capacitors connected in parallel with theswitching tubes are parasitic devices or external devices of theswitching tubes.

Preferably, the DC-DC converter further includes an output filter; theoutput filter includes a filter inductor and a filter capacitor;

the filter inductor has one end connected to a first terminal of theoutput end of the rectifier module, and the other end serving as a firstterminal of the DC output end of the DC-DC converter;

the filter capacitor has one end connected to the other end of thefilter inductor and the other end connected to a second terminal of theoutput end of the rectifier module, the other end of the filtercapacitor serving as a second terminal of the DC output end of the DC-DCconverter.

Preferably, the DC-DC converter further includes a converter filtercapacitor which is connected in parallel to the first bridge armtopology and used for smoothing a voltage.

In general, by comparing the above technical solution of the presentinventive concept with the prior art, the present invention has thefollowing beneficial effects:

1. by utilizing the structural characteristics, an inductor L1 and ahalf bridge (that is, the second bridge arm topology formed by thesecond switching tube (Q2) and the fifth switching tube (Q5) in series)are multiplexed, so that the converter can be made compact, whichreduces the cost, and the number of switching tubes is reduced, thusreducing the switching loss under the same operating conditions.

2. soft switching of each switching tube is achieved, and MOSFETs areused instead of diodes in the general Buck converter to achievesynchronous rectification. Through the soft switching technology andsynchronous rectification technology, switching loss and on-state lossare reduced, thereby improving the efficiency of the converter.

3. by reducing the switching loss, the switching frequency can begreatly increased. This not only improves the output waveform, but alsoreduces the filtering difficulty and reduces the volume of the filter.In addition, when the voltage frequency is increased, the transformer isno longer so easily saturated, and then the volume of the transformercan be reduced. Therefore, the present invention can achieve higherconversion efficiency while increasing the power density to a greaterextent.

4. by reasonable application of the multi-stage series structure, a wideDC input range is achieved, and a large multiple of buck can beachieved, which is adapted to application requirements

5. The invention can realize multiple input and output ports, and thuscan be applied to occasions requiring multiple voltage levels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a DC-DC converter topology according to the present invention;and

FIG. 2 is a frame diagram of a typical peripheral circuit of the DC-DCconverter topology according to the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention is further described below in conjunction withembodiments and the accompanying drawings, which is illustrative but notlimitative of the present invention.

The present invention provides a DC-DC converter topology with threeports, which can be used in a DC power supply place. The topology makesfull use of the structural characteristics of the converter to multiplexthe devices, which saves the cost, and introduces synchronousrectification technology, which reduces on-state voltage drop andon-state loss. Meanwhile, soft switching is achieved for all switchingtubes to reduce the switching loss, which can increase the switchingfrequency and ensure the efficiency of the device. In addition, due tothe multi-stage conversion, multiple DC output ports are provided, andthrough rational design, the converter topology has a wide range of DCinput and can achieve a large multiple of buck.

The DC-DC converter topology according to the present inventionsuccessively includes, as shown in FIG. 1, a converter filter capacitorC7, a Buck converter, a Boost converter and a phase-shifted full-bridgeconverter, when seen from the main input port. The converter filtercapacitor is used for smoothing the voltage,

As shown in FIG. 1, a capacitor C8 is connected in parallel at an inputend of the phase-shifted full-bridge converter, that is, an output endof the Boost converter to virtualize a DC bus. The virtualized DC buscan be used as an input port or as an output port. The phase-shiftedfull-bridge converter includes an inverter bridge and a rectifiermodule, and the output end of the rectifier module is another DC outputport of the topology.

In the topology, the Buck converter portion is composed of a firstbridge arm topology formed by a first switching tube Q1 and a fourthswitching tube Q4 in series, and an inductor L1. The inductor L1 has oneend connected to a coupling point formed by connecting the firstswitching tube Q1 and the fourth switching tube Q4 in series. In theBuck converter circuit portion, MOSFETs are used instead of diodes toachieve synchronous rectification, and the switching tubes can also useother types of switching tubes.

The Boost converter portion is composed of a second bridge arm topologyformed by the inductor L1, a second switching tube Q2 and a fifthswitching tube Q5 in series, and a capacitor C8. The inductor L1 has theother end connected to a coupling point formed by connecting the secondswitching tube Q2 and the fifth switching tube Q5 in series. Thecapacitor C8 is connected between positive and negative input ports ofthe Boost converter. Similarly, MOSFETs are used instead of diodes inthe general Boost converter. The Buck converter and the Boost converterare connected in series to form the front-stage DC-DC converter, andthey share the inductor L1. The inductor L1 can be a single inductor oran equivalent inductor formed by multiple inductors.

The phase-shifted full-bridge converter portion is composed of thesecond bridge arm topology formed by the second switching tube Q2 andthe fifth switching tube Q5 in series, a third bridge arm topologyformed by a third switch transistor Q3 and a sixth switch transistor Q6in series, a resonant inductor L2, a DC blocking capacitor C10 and arectifier module. The rectifier module includes a transformer T1 anddiodes D7 and D8. The second bridge arm topology serves as a leading legof the phase-shifted full-bridge converter, and the third bridge armtopology serves as a lagging leg of the phase-shifted full-bridgeconverter. The resonant inductor L2 includes the leakage inductance ofthe transformer. The primary side of the transformer T1 is connected inseries to the resonant inductor L2 and the DC blocking capacitor C10,and two ends of this series branch are respectively connected to thecoupling point formed by connecting the second switching tube Q2 and thefifth switching tube Q5 in series and the coupling point formed byconnecting the third switching tube Q3 and the sixth switching tube Q6in series. Two ends of the secondary side of the transformer T1 arerespectively connected in series with the diodes D7 and D8, and theother ends of the two diodes are connected together. A coupling pointformed by connecting the diodes D7 and D8 serves as a first terminal ofthe output end of the phase-shifted full-bridge converter, and a centertap of the transformer T1 serves as a second terminal of the output endof the phase shifted full bridge converter.

The DC-DC converter further includes a filter inductor L3 and a filtercapacitor C9. The filter inductor L3 is connected to the coupling pointformed by connecting the diodes D7 and D8, and is also connected inseries to the filter capacitor C9 and the center tap of the secondaryside of the transformer T1. The filter inductor L3 and the filtercapacitor C9 constitute an output filter, which is a low pass filter.Two end of the filter capacitor C9 serve as an output port of the DC-DCconverter.

It can be seen that the Buck converter portion and the phase-shiftedfull-bridge converter portion multiplex the second bridge arm topologyformed by the second switching tube Q2 and the fifth switching tube Q5in series, so that the converter can be made compact, which reduces thecost, and the number of switching tubes is reduced, thus reducing theswitching loss under the same operating conditions.

In addition, each switching tube is reversely connected in parallel witha diode, and also is connected in parallel with a capacitor. The diodesand capacitors can be parasitic devices of the switching tubes, or canbe external independent devices. With these diodes and capacitors,zero-voltage switching (ZVS) can be achieved.

The working principle of soft switching achieved by the Buck converteris as follows: the working mode of the Buck converter portion in thistopology is inspected, and since each switching tube is connected inparallel with a capacitor, when the switching tube is switched from ONstate to OFF state, the voltage across the switching tube will riserelatively slowly, so that the higher switching current is staggered,thereby achieving zero voltage turn-off and reducing the turn-off loss.When the switching tube is switched from OFF state to ON state, due tothe resonance formed by the capacitor and the inductor, the voltageacross the capacitor will pass 0V. At this time, the diode is turned on,the voltage across the switching tube is clamped at 0V, and thus, theswitching tube can be turned on at zero voltage, thereby achieving zerovoltage turn-on and reducing the turn-on loss. The above is the softswitching implementation of the Buck circuit. In order to ensure theimplementation of the soft switching of the front-stage Buck converter,the inductor current needs to be able to drop to OA. Therefore, thevalue of the inductor can be reasonably designed to operate thefront-stage DC-DC converter in the discontinuous mode (DCM).

The Boost circuit portion and the phase-shifted full-bridge converterportion in the DC-DC converter topology share the bridge arm formed bythe second switching tube Q2 and the fifth switching tube Q5 in series.Since the bridge arm of the phase-shifted full bridge converter adoptsphase shifting control and the duty cycle of the switching tube of theinverter bridge is fixed, the duty cycle D of the Boost converter isalso fixed. Considering that the Boost converter is also in thediscontinuous mode, the actual transformation ratio will be greater than1/(1−D).

The phase-shifted full-bridge converter portion in the DC-DC convertertopology realizes the adjustment of the output voltage through phaseshifting control, and all the switching tubes on the inverter bridge canrealize soft switching.

The input end of the phase-shifted full bridge converter receives a DCinput (in this topology, the output of the Boost converter), an ACbridge arm voltage is obtained through the inverter bridge, and thenoutput to the primary side of the transformer. The transformer canprovide a transformer ratio, and a center tap and rectifier diodes areprovided on the secondary side of the inverter, thereby achievinguncontrolled rectification.

Through phase shifting control of the two half bridges of the inverterbridge, there is an adjustable phase difference between control signalsof the two half bridges, and by controlling this phase difference, theduty ratio of the output voltage can be controlled, thereby controllingthe magnitude of the output voltage. Therefore, in the two half bridges,the second bridge arm consisting of the second switching tube Q2 and thefifth switching tube Q5 is called a leading leg, and the third bridgeconsisting of the third switching tube Q3 and the sixth switching tubeQ6 is called a lagging leg. Between the two half bridges, in addition tothe rectifier module, a resonant inductor L2 and a DC blocking capacitorC10 are connected in series. The resonant inductor and the capacitorsconnected in parallel at both ends of the switching tubes form aresonance under a certain operating mode, thereby enabling zero-voltageswitching of the switching tubes.

The soft switching of the phase-shifted full-bridge circuit is realizedas follows: when the switching tube is switched from ON state to OFFstate, the voltage across the switching tube will rise relatively slowlydue to capacitor charging, so that the higher switching current isstaggered, thereby achieving zero voltage turn-off and reducing theturn-off loss. When the switching tube is switched from OFF state to ONstate, due to the resonance formed by the capacitor and the inductor,the voltage across the capacitor will drop to 0V at a certain moment. Atthis time, the diode is turned on, the voltage across the switching tubeis clamped at 0V, and thus, the switching tube can be turned on at zerovoltage, thereby achieving zero voltage turn-on and reducing the turn-onloss.

For clearer description of the present invention, a typical peripheralcircuit of the DC-DC converter is illustrated in FIG. 2, and includes amain processor module, a sampling module, a driving module and aconditioning module. The output of the Buck converter is sampled by thesampling module, processed by the conditioning circuit, and then inputto the processor. According to a designed program, the processor outputsa control signal to the driving module so as to drive the firstswitching tube Q1 and the fourth switching tube to perform synchronousoperation and complementary switching. In order to avoid theshoot-through state, dead bands can be provided for the first switchingtube Q1 and the fourth switching tube Q4. Meanwhile, the output of therectifier module is sampled, processed by the conditioning module, andthen input to the processor. According to the control program designedin the processor, the processor obtains the phase shifting magnitude andoutputs a control signal to the driving module, and then the drivingmodule outputs a driving signal to control on/off of the switching tubesin the second bridge arm topology and the third bridge arm topology,thereby constituting a closed loop containing the controller.

In the present invention, the front-stage DC-DC converter is formed bythe Buck converter and the Boost converter in series, and is a direct DCconverter, while the back-stage converter is a phase-shifted full-bridgeconverter including an inverter bridge and a rectifier converter as wellas an isolated transformer, and is an indirect DC converter.

The topology makes full use of the structural characteristics of theconverter to multiplex the devices, which saves the cost, and introducessynchronous rectification technology, which reduces on-state voltagedrop and on-state loss. Meanwhile, soft switching is achieved for allswitching tubes to reduce the switching loss, which can increase theswitching frequency and ensure the efficiency of the device. Inaddition, due to the multi-stage conversion, multiple DC output portsare provided, and through rational design, the converter topology has awide range of DC input and can achieve a large multiple of buck.

It should be readily understood to those skilled in the art that theabove description is only preferred embodiments of the presentinvention, and does not limit the scope of the present invention. Anychange, equivalent substitution and modification made without departingfrom the spirit and scope of the present invention should be includedwithin the scope of the protection of the present invention.

What is claimed is:
 1. A DC-DC converter, characterized by comprising:an inductor, a rectifier module, a first bridge arm topology and asecond bridge arm topology and a third bridge arm topology in parallelas well as a capacitor, wherein the first bridge arm topology includes afirst switching tube and a fourth switching tube in series, the secondbridge arm topology includes a second switching tube and a fifthswitching tube in series, and the third bridge arm topology includes athird switching tube and a sixth switching tube in series; a negativepole of the first bridge arm topology is connected to a negative pole ofthe second bridge arm topology, and the inductor has one end connectedto a coupling point formed by connecting the first switching tube andthe fourth switching tube in series, and the other end connected to acoupling point formed by connecting the second switching tube and thefifth switching tube in series; an input end of the rectifier module hasone end connected to the coupling point formed by connecting the secondswitching tube and the fifth switching tube in series, and the other endconnected to a coupling point formed by connecting the third switchingtube and the sixth switching tube in series, and the rectifier module isused to convert an alternating current into a direct current; there is aphase difference between a control signal of the second bridge armtopology and a control signal of the third bridge arm topology; thefirst bridge arm topology and the inductor constitute a Buck converterfor stepping down an input voltage, the second bridge arm topology andthe inductor constitute a Boost converter for stepping up an inputvoltage, and the second bridge arm topology, the third bridge armtopology and the rectifier module constitute a phase-shifted full-bridgeconverter for stepping down or stepping up an input voltage; the DC-DCconverter multiplexes the inductor and the second bridge topology. 2.The DC-DC converter of claim 1, characterized in that two ends of thefirst bridge arm topology serve as an DC input end of the DC-DCconverter, the capacitor serves as a first DC output end of the DC-DCconverter, and an output end of the rectifier module serves as a secondDC output end of the DC-DC converter.
 3. The DC-DC converter of claim 1,characterized in that two ends of the first bridge arm topology serve asa first DC input end of the DC-DC converter, the capacitor serves as asecond DC input end of the DC-DC converter, and an output end of therectifier module serves as a first DC output end of the DC-DC converter.4. The DC-DC converter of claim 1, characterized in that the rectifiermodule comprises a transformer and two rectifier diodes, a primary sideof the transformer serves as the input end of the rectifier module, tapson both ends of a secondary side of the transformer are each connectedin series with a rectifier diode, the other ends of the two rectifierdiodes are connected as a first port of the output end of the rectifiermodule, and a center tap of the transformer serves as a second port ofthe output end of the rectifier module.
 5. The DC-DC converter of claim1, characterized in that each of the switching tubes of the first bridgearm topology is connected in parallel with a diode and a capacitor toenable soft switching of the switching tubes in the first bridge armtopology.
 6. The DC-DC converter of claim 5, characterized in that thediodes and capacitors connected in parallel with the switching tubes areparasitic devices or external devices of the switching tubes.
 7. TheDC-DC converter of claim 1, characterized by further comprising aresonant inductor and a DC blocking capacitor, wherein the resonantinductor, the primary coil of the transformer and the DC blockingcapacitor are sequentially connected in series to form a series branch,the series branch has one end connected to the coupling point formed byconnecting the second switching tube and the fifth switching tube inseries and the other end connected to the coupling point formed byconnecting the third switching tube and the sixth switching tube inseries, and each of the switching tubes of the second bridge armtopology and the third bridge arm topology is connected in parallel witha diode and a capacitor to enable soft switching of each of theswitching tubes of the second bridge arm topology and the third bridgearm topology.
 8. The DC-DC converter of claim 1, characterized in thatthe DC-DC converter further includes an output filter; the output filterincludes a filter inductor and a filter capacitor; the filter inductorhas one end connected to a first terminal of the output end of therectifier module, and the other end serving as a first terminal of theDC output end of the DC-DC converter; the filter capacitor has one endconnected to the other end of the filter inductor and the other endconnected to a second terminal of the output end of the rectifiermodule, the other end of the filter capacitor serving as a secondterminal of the DC output end of the DC-DC converter.
 9. The DC-DCconverter of claim 1, characterized in that the DC-DC converter furtherincludes a converter filter capacitor which is connected in parallel tothe first bridge arm topology and used for smoothing a voltage.